The present invention relates generally to apparatus and methods for the autotransfusion of blood. Particularly, the present invention relates to apparatus and methods for high speed processing, cleansing and reconstituting a patient's blood during operation procedures prior to returning the blood to that patient.
During and after surgery, blood is removed from the body of the patient. This blood includes healthy red and white blood cells, platelets, and blood plasma (the fluid portion of the blood) along with solid and particulate refuse resulting from the operation itself. The refuse may include the cell walls of red blood cells which have been damaged or ruptured, platelets, leukocyte aggregates, small pieces of tissue, blood clots as well as other undesirable substances. The blood removed from a patient cannot immediately be returned to the patient because of this refuse in the blood, but it is desirable to return the patient's blood rather than to supply additional blood for a number of reasons.
It is desirable to remove the blood from the patient, process it to remove the refuse and plasma, wash the remaining blood cells to remove anticoagulant, and quickly return the healthy red blood cells to the patient. If not washed, the anticoagulant builds up in the patient and causes severe problems. In the past, the blood was first filtered to remove some of the particulate refuse. The remaining whole blood was then centrifuged to separate plasma and other body fluids from red blood cells which could then be washed with a washing solution and centrifuged again to separate washing solution from the red blood cells. This process was very slow which prevented the reintroduction of a patient's own blood back to the patient during and after the surgical procedure. As a result, separate supplies of blood were needed. This raised the problems sufficient separate blood supplies free of disease-causing contaminants.
The uninterrupted process of removing a patient's blood from the patient's body, processing the blood and returning healthy red blood cells in an on-line manner is referred to herein "autotransfusion." U.S. Pat. No. 4,631,050 describes an autotransfusion device utilizing membrane filtration techniques. The device of this patent describes mixing a washing solution into the whole blood after an initial filtration to remove gross debris followed by a one-stage membrane filtration of the plasma and washing solution from the blood. No system is disclosed which separates the plasma from the whole blood prior to washing. A preferred sequence is to remove the plasma and other body fluids, wash the red blood cells and remove the washing solution. This sequence enhances fluid removal and washing of anticoagulant from the blood cells. The patent fails to disclose a means of preventing build- up of red blood cells along the membrane filter which, if not avoided, eventually results in clogging of the membrane filter.
Attempts to solve the problem of cell buildup are shown in U.S. Pat. Nos. 4,713,176, 4,670,147, and 4,675,106, which describe means of preventing build-up of red blood cells along a filter membrane due to Taylor Vortex action. They also fail to disclose a system which separates the plasma from the whole blood prior to washing and require a rotating hollow cylinder covered by a membrane filter to accomplish the filtration. No additional filtration capability is disclosed. Further, the prior art discloses apparatus and methods from the simple separation of biological cells from liquids but not a successful autotransfusion device which provides for the cleaning of red blood cells in a continuous manner. One such solution to the problem appears in European patent application No. 87302368.3, filed Mar. 19, 1987, belonging to Toray Industries, which discloses a rotating disc to impart shearing forces to blood cells during plasma phoresis. It fails, however to describe a solution to the problem unique to autotransfusion; i.e., the washing of anticoagulant from the blood cells before returning to the operative patient.
It is an object of this invention to provide an autotransfusion system using a two-stage filter which provides for a saline wash step between the filtration steps to better remove anticoagulant from blood cells.
An advantage of the system of the invention is accomplished with a filter which receives blood cells in whole blood and initially concentrates the cells by removing at least a portion of the plasma and other fluids through a first flat membrane, then washes the blood cells removing additional impurities and anticoagulant and dilutes the partially concentrated cells with a washing solution, and then removes the washing solution along with additional plasma and other fluids through a second flat membrane. The blood cells are then removed and can be returned directly to a patient.